Nowadays, the existence of high entropy perovskite (HEP) oxides is well established and, since their discovery, they have found application in several technological fields. The main advantage provided by these materials, with the general formula ABO₃, is the possibility of widely tuning their properties by acting on the chemical composition. The study of stability, fields of existence, and solubility limits in a systematic way remains lacking in comparison with continuous application research, despite the presence of large datasets and computational studies. In the present work, we aimed at investigating the structure and solubility limits of two series of HEPs including five different cations on the perovskite B-site, namely La(CrMnFeCoNi)O₃ and La(CrMnFeCoZn)O₃, exploring a full range of compositions beyond the classical equimolar phases usually investigated. This has been accomplished by the design of experiment strategy to investigate the influence of the B-site composition on phase stability, crystal structure, and oxygen non-stoichiometry for the two systems providing a solid tool for researchers to predict such properties on the whole compositional space of the two HEPs.